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United States Patent |
5,720,166
|
Toshiro
,   et al.
|
February 24, 1998
|
Fuel supply control device for an engine
Abstract
An engine is equipped with a mechanism for supplying supplementary air into
an exhaust conduit upstream of a catalytic converter in order to increase
catalytic activity thereof. An incremental proportion for fuel supply
during this supply of supplementary air is determined so as to keep the
concentration of oxygen upstream of the catalytic converter substantially
at a predetermined value which corresponds to an air/fuel ratio on the
lean side of stoichiometric. Further, the amount of fuel supplied is
corrected according to the greater of this incremental proportion and an
incremental proportion which is determined according to the temperature of
the engine. By doing this, the oxygen concentration in the vicinity of the
intake of the catalytic converter is maintained at the predetermined value
which is lean, and the catalyst is activated at an early stage.
Inventors:
|
Toshiro; Takayuki (Fujisawa, JP);
Mori; Koichi (Sagamihara, JP);
Nishizawa; Kimiyoshi (Yokohama, JP)
|
Assignee:
|
Nissan Motor Co., Ltd. (Yokohama, JP)
|
Appl. No.:
|
622395 |
Filed:
|
March 27, 1996 |
Foreign Application Priority Data
Current U.S. Class: |
60/284; 60/285 |
Intern'l Class: |
F02D 041/08; F01N 003/20 |
Field of Search: |
60/284,285
|
References Cited
U.S. Patent Documents
3949551 | Apr., 1976 | Eichler et al. | 60/284.
|
5483946 | Jan., 1996 | Hamburg et al. | 60/284.
|
5584176 | Dec., 1996 | Meyer et al. | 60/284.
|
Foreign Patent Documents |
6-81696 | Mar., 1994 | JP.
| |
Primary Examiner: Argenbright; Tony M.
Attorney, Agent or Firm: Foley & Lardner
Claims
We claim:
1. A fuel supply control device, fitted to an engine which comprises an
exhaust conduit, a catalytic converter provlded in said exhaust conduit,
and means for selectively feeding supplementary air into said exhaust
conduit on the upstream side of said catalytic converter, comprising:
means for detecting a warming-up state of said engine;
means for determining a first incremental proportion for fuel supply amount
for said engine according to said warming-up state of said engine;
means for detecting said feeding in of supplementary air;
means for detecting the idling operational state of said engine;
means for, when both said feeding in of supplementary air and said engine
idling operational state are detected, determining a second incremental
proportion for fuel supply amount for said engine in correspondence to
said feeding in of supplementary air, so as to keep the concentration of
oxygen at the upstream slde of said catalytic converter substantially at a
predetermined value which corresponds to an air/fuel ratio on the lean
slde of stoichiometric;
means for determining a final incremental proportion by selecting the
larger one of said first and said second incremental proportion; and
means for correcting a fuel supply amount for said engine according to said
final incremental proportion.
2. A fuel supply control device according to claim 1, further comprising
means for detecting the amount of air inhaled by said engine, and wherein
said second incremental proportion determination means comprises means for
calculating said second incremental proportion based upon said amount of
air inhaled by said engine, a feeding in amount of supplementary air, and
said predetermined value.
3. A fuel supply control device according to claim 2, wherein said second
incremental proportion determination means further comprises means for
limiting said calculated second incremental proportion to a previously
determined upper limit.
4. A fuel supply control devlce according to claim 1, wherein said second
incremental proportion determination means determines said second
incremental proportion according to the warming-up state of said engine.
5. A fuel supply control device, fitted to an engine which comprises an
exhaust conduit, a catalytic converter provlded in said exhaust conduit,
and means for selectively feeding supplementary air into said exhaust
conduit on the upstream side of said catalytic converter, comprising:
means for detecting a warming-up state of said engine;
means for determining a first incremental proportion for fuel supply amount
for said engine according to said warming-up state of said engine;
means for detecting said feeding in of supplementary air;
means for detecting in idling operational state of said engine;
means for, when both said feeding in of supplementary air and said engine
idling operational state are detected, determining a target value for a
second incremental proportion for fuel supply amount for said engine in
correspondence to said feeding in of supplementary air, so as to keep the
concentration of oxygen at the upstream side of said catalytic converter
substantially at a predetermined value which corresponds to an air/fuel
ratio on the lean side of stoichiometrlc;
means for gradually changing said second incremental proportion in the
direction of said target value along wlth the passage of time from the
determination of said target value;
means for determining a final incremental proportion by selecting the
larger one of said first and said second incremental proportion; and
means for correcting a fuel supply amount for said engine according to said
final incremental proportion.
Description
FIELD OF THE INVENTION
This invention relates to fuel supply control when supplementary air is fed
into an exhaust passage of an engine upstream of a catalytic converter.
BACKGROUND OF THE INVENTION
When an engine is running in the idling state and its temperature is low,
the air-fuel ratio of the fuel mixture supplied to the engine is enriched
and supplementary air is fed into the exhaust passage upstream of a
catalytic converter thereof, CO and HC in the exhaust gas combine with the
oxygen contained in this supplementary air, and it is per se known that
the activity of the catalyst is increased by the heat of oxidation.
However, if the air/fuel ratio is enriched too much, irregularity in the
rotation of the engine and misfiring may occur.
In this connection the concept was disclosed in Tokkal Hei 6-81696
published by the Japanese Patent Office in 1994, of detecting the level of
stability of the engine during the supply of supplemental air from
irregularity in the rotation of the engine, and of increasing the supply
of fuel so as to enrich the air/fuel ratio, only when this stability so
permits.
However, if increase of the amount of fuel is only dependent upon the
stability in operation of the engine, it can happen that the balance
between the amount of fuel increase and the amount of supplementary air
becomes confused and the amount of supplementary air becomes insufficient,
so that the oxidation reaction is not performed adequately.
Further, generally the amount of fuel supplied to an engine should be
increased when the temperature of its coolant is low, i.e. so called
coolant temperature compensation should be performed. When this coolant
temperature compensation and the compensation quantity for catalyst
activity increase are combined, the air/fuel ratio is enriched further.
When this is done, if the oxidizing reaction does not occur adequately, to
that extent the increase in activity of the catalyst undesirably lags.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to prevent excessive enrichment
of the air/fuel ratio when supplementary air is fed into the exhaust
passage.
It is a further object of this invention to prevent delay in increase of
the activity of the catalyst due to an excessive degree of enrichment of
the air/fuel ratio when supplementary air is fed into the exhaust passage.
In order to achieve the above objects, this invention provides a fuel
supply control device fitted to such an engine that comprises an exhaust
conduit, a catalytic converter provided in said exhaust conduit, and a
mechanism for selectively feeding supplementary air into the exhaust
conduit on the upstream side of the catalytic converter. The control
device comprises a mechanism for detecting a warming-up state of the
engine, a mechanism for determining a first incremental proportion for
fuel supply amount for the engine according to the warming-up state of the
engine, a mechanism for detecting the feeding in of supplementary air, a
mechanism for detecting the idling operational state of the engine, a
mechanism for, when both the feeding in of supplementary air and the
engine idling operational state are detected, determining a second
incremental proportion for fuel supply amount for the engine in
correspondence to the feeding in of supplementary air, so as to keep the
concentration of oxygen at the upstream side of the catalytic converter
substantially at a predetermined value which corresponds to an air/fuel
ratio on the lean side of stoichiometric, a mechanism for determining a
final incremental proportion by selecting the larger one of the first and
the second incremental proportion, and a mechanism for correcting a fuel
supply amount for the engine according to the final incremental
proportion.
It is preferable that the control device further comprises a mechanism for
detecting the amount of air inhaled by the engine, and the second
incremental proportion determination mechanism comprises a mechanism for
calculating the second incremental proportion based upon the amount of air
inhaled by the engine, a feed in amount of the supplementary air, and the
predetermined value.
It is further preferable that the second incremental proportion
determination mechanism further comprises a mechanism for limiting the
calculated second incremental proportion to a previously determined upper
limit.
It is also preferable that the second incremental proportion determination
mechanism determines the second incremental proportion according to the
warming-up state of the engine.
According to another aspect of this invention, the control device comprises
a mechanism for detecting a warming-up state of the engine, a mechanism
for determining a first incremental proportion for fuel supply amount for
the engine according to the warming-up state of the engine, a mechanism
for detecting the feeding in of supplementary air, a mechanism for
detecting in idling operational state of the engine, a mechanism for, when
both the feeding in of supplementary air and the engine idling operational
state are detected, determining a target value for a second incremental
proportion for fuel supply amount for the engine in correspondence to the
feeding in of supplementary air, so as to keep the concentration of oxygen
at the upstream side of the catalytic converter substantially at a
predetermined value which corresponds to an air/fuel ratio on the lean
side of stoichiometric, a mechanism for gradually changing the second
incremental proportion in the direction of the target value along with the
passage of time from the determination of the target value, a mechanism
for determining a final incremental proportion by selecting the larger one
of the first and said second incremental proportion, and a mechanism for
correcting a fuel supply amount for the engine according to the final
incremental proportion.
The details as well as other features and advantages of this invention are
set forth in the remainder of the specification and are shown in the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an engine to which a fuel supply control
device according to a first embodiment of this invention is fitted.
FIG. 2 is a flow chart showing a process for calculating fuel injection
amount, according to the first embodiment of this invention.
FIG. 3 is a flow chart showing a process for calculating a supplementary
air incremental proportion KAP, according to the first embodLment of this
invention.
FIG. 4 is a flow chart showing a process of calculating the supplementary
air incremental proportion KAP, according to a second embodiment of this
invention.
FIG. 5 is similar to FIG. 2, but showing a third embodiment of this
invention.
FIG. 6 is a diagram showing variation of a fuel increase amount ratio, for
the third embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 of the drawings, a multi cylinder liquid cooled engine
1 inhales air from an air cleaner 2 via an intake passage 3. The amount of
inhaled air is controlled by a throttle valve 4. The intake passage 3 is
connected to each cylinder of the engine 1 vla an intake manifold 3A. For
each cylinder, a fuel injection valve 5 is provlded within the intake
manifold 3A, and each of these fuel injection valves 5 injects fuel into
the air which is being inhaled into its corresponding cylinder.
The fuel injection valves 5 are electromagnetic type fuel injection valves
which inject fuel under the control of drive signals which are supplied to
them from a control unit 10, and the amount of fuel which they inject
corresponds to the pulse width of these drive signals. Accordingly, the
air/fuel ratio of the mixture gas which is supplied to the engine 1 can be
varied by this pulse width.
The mixture gas in each of the cylinders of the engine 1 is ignited by a
spark plug not shown in the figure and undergoes combustion, and the
resulting exhaust gas is discharged via an exhaust manifold 6A which is
connected to the cylinders into an exhaust conduit 6.
Part way along the exhaust conduit 6 there is interposed a catalytic
converter 7 which uses a three way catalyst and which purifies the exhaust
gas of harmful components such as HC, CO, and NOx contained therein by
oxidation and reduction thereof.
A supplementary air feed conduit 9 is connected to the exhaust condult 6
upstream of the catalytic converter 7, and feeds supplementary air
thereinto. Air is supplied into this supplementary air feed conduit 9 by
an electrically driven air pump 8. The operation of this air pump 8 is
controlled in an on and off manner by a signal which is output from the
control unit 10, and when the air pump 8 is operating it suppiles a
constant flow Qap of supplementary air into the supplementary air feed
conduit 9.
In order for the control unit 10 to control the amount of fuel injection
performed by the fuel injection valves 5, signals are supplied to it from
an air flow meter 11, a crank angle sensor 12, a coolant temperature
sensor 13, and an idle switch 14.
The air flow meter 11 is provided upstream of the throttle valve 4 in the
intake passage 3, and measures the inhaled air flow Q.
The crank angle sensor 12 outputs a standard position signal when the
crankshaft (not shown) of the engine 1 is in a predetermined standard
rotational positions corresponding to a specific piston position of
respective cylinder, and also outputs a much finer unit crank angle signal
every time the crankshaft moves through a predetermined rotational angle,
e.g., one degree.
The coolant temperature sensor 13 is fitted into the coolant jacket which
contains the coolant for the engine 1, and outputs a coolant temperature
signal Tw.
The idle switch 14 outputs an on signal when the throttle valve 4 is fully
closed, in order to indicate that the engine 1 is in the idling state.
The control unit 10 comprises a microcomputer, which calculates a fuel
injection amount Ti according to the process shown in FIG. 2 based upon
the output signals from the various sensors described above, and outputs
drive signals having pulse widths corresponding to this value Ti to the
fuel injection valves 5 at timings synchronized with the rotation of the
crankshaft of the engine 1.
To explain this process, first in the step S1 of FIG. 2 a basic fuel
injection amount Tp for the current inhaled air flow Q corresponding to
the stoichiometric air/fuel ratio is calculated according to the following
equation from the inhaled air amount Q obtained from the air flow meter 11
and the engine revolution speed N obtained from the output signal of the
crank angle sensor 12:
##EQU1##
where K is a constant.
In the step S2, a coolant temperature incremental proportion KTW, which is
a first incremental proportion based upon the coolant temperature Tw, is
determined by looking up an internally stored map. This coolant
temperature incremental proportion KTW is a value which is determined by
this map as being the greater, the lower is the coolant temperature Tw.
In the step S3, a decision is made as to whether or not the air pump 8 is
on, i.e. as to whether or not supplementary air is currently being fed
into the exhaust condult 6, and if the air pump 8 is on then the flow of
control continues to the step S4.
In the step S4, a decision is made as to whether or not the idle switch 14
is on, and if it is on then the flow of control continues to the step S5.
Accordingly, the flow of control only reaches the step S5 if supplementary
air is being provided and also the engine is idling.
In the step S5, a supplementary air incremental proportion KAP, which is a
second incremental proportion, is calculated so as to make the oxygen
concentration in the exhaust conduit 6 at the intake of the catalytic
converter 7 leaner than the value which corresponds to the stoichiometric
air/fuel ratio, i.e. so as to make the excess air ratio .lambda. greater
than 1.
This calculation process is shown in FIG. 3.
In the step S101, the supplementary air incremental proportion KAP is
calculated from the inhaled air flow Q, the constant supplementary air
flow Qa, and the target excess air ratio .lambda. at the intake of the
catalytic converter 7, according to the following equation:
##EQU2##
In the next step S102, the calculated value for the supplementary air
incremental proportion KAP and an upper limit value therefor which is
determined in advance are compared, and if the calculated value for KAP is
greater than this upper limit value then KAP is set to the upper limit
value. This is done in order not to provoke misfiring, which might be
caused by too much enrichment of the air/fuel ratio. If the calculated
value for KAP is not greater than the upper limit value then it is used
without any alteration. Finally the flow of control returns from this
subroutine.
If on the other hand the result of the decision in the step S3 is that the
air pump 8 is off, or if the result of the decision in the step S4 is that
the idle switch 14 is off, then the flow of control is transferred to the
step S6, in which the supplementary air incremental proportion KAP is set
to zero.
In the step S7, the final incremental proportion KM is calculated as being
the greater of the coolant temperature incremental proportion KTW and the
supplementary air incremental proportion KAP, i.e. according to the
following equation:
KM=MAX(KTW, KAP)
In the step S8, the final fuel injection amount Ti is calculated by
correcting the basic fuel injection amount Tp according to the following
equation:
Ti=Tp.multidot.(1+KM)
Various other corrections may be applied during the calculation of the
final fuel injection amount Ti, such as an acceleration correction, an
air/fuel ratio feedback correction, a battery voltage correction, etc.,
but no explanation will be provided regarding such additional corrections
because they are not relevant to this invention.
The calculated final fuel injection amount Ti is written into a
predetermined register in the control unit 10, and drive signals having
pulse widths corresponding to this value Ti are output at predetermined
fuel injection timing points to the fuel injection valves 5, so as to
perform fuel injection.
Since, in this manner, during engine idling when supplementary air is being
supplied, the supplementary air incremental proportion KAP is set so as to
make the oxygen concentration at the intake of the catalytic converter 7
leaner than the value which corresponds to the stoichiometric air/fuel
ratio, and the greater one of this value KAP and the coolant temperature
incremental proportion KTW is utilized for correction of the amount of
fuel to be injected, thereby, although the oxygen concentration at the
intake of the catalytic converter 7 is lean, it is maintained in a range
which has no tendency to become very lean. Accordingly, on the one hand a
sufficient quantity of air is supplied for the oxidation reaction, while
on the other hand it is ensured that the quantity of air supplied does not
become too great (which would cool down the catalyst), so that it is
possible efficiently to increase the activity of the catalyst by elevating
its temperature.
FIG. 4 shows a second embodiment of this invention. In this second
embodiment, a map is constructed which determines the supplementary air
incremental proportion KAP according to the coolant temperature Tw, in
order to keep the oxygen concentration at the intake of the catalytic
converter 7 leaner than the value which corresponds to the stoichiometric
air/fuel ratio. When deriving the supplementary air incremental proportion
KAP, rather than calculating it by executing the process shown in FIG. 3,
instead the value of the supplementary air incremental proportion KAP is
looked up from this map. Moreover, KAP is set to be the greater, the
higher is the coolant temperature Tw.
It would also be possible to determine the supplementary air incremental
proportion KAP according to the coolant temperature when stating the
engine Tws, instead of according to the coolant temperature Tw.
FIG. 5 shows a third embodiment of this invention. In this third
embodiment, the process shown in FIG. 5 is executed for calculating the
fuel injection amount, instead of the process shown in FIG. 2.
The steps S11 through S15 are the same as the steps S1 through S5 of FIG.
2.
However, in this embodiment, the value of the supplementary air incremental
proportion KAP calculated in the step S15 is considered as a target
supplementary air incremental proportion. In this third embodiment, the
calculated air incremental proportion KAP in the step S15 is not utilized
directly for the determination of the final incremental proportion KM;
instead, the final incremental proportion KM is increased each time by a
predetermined value .DELTA.KAP, and this is in order to attain the target
supplementary air incremental proportion KAP.
In order to do this, in the step S16 a supplementary air incremental
proportion MKAP is determined according to the following equation:
MKAP=KM+.DELTA.KAP
In the step S17, the supplementary air incremental proportion MKAP and the
target supplementary air incremental proportion KAP are compared.
If MKAP>KAP, then in the step 818 the supplementary air incremental
proportion MKAP is set equal to KAP.
If the result of the decision in the step S13 is that the air pump 8 is
off, or if the result of the decision in the step S14 is that the idle
switch 14 is off, then the flow of control is transferred to the step S19.
Here, instead of immediately setting the incremental proportion to zero as
was done in the step S6, it is reduced each time by the predetermined
value .DELTA.KAP as shown by the following equation:
MKAP=KM-.DELTA.KAP
The steps S20 and S21 are the same as the steps S7 and S8 of FIG. 2.
In this third embodiment, as shown in FIG. 6, when the condition holds that
supplementary air is being suppiled and also the engine is idling, the
final incremental proportion KM is gradually increased until it reaches
the supplementary air incremental proportion KAP which makes the oxygen
concentration at the intake of the catalytic converter 7 to be a
predetermined value somewhat upon the lean slde. On the other hand, if
this condition stops holding, then the final incremental proportion KM is
gradually decreased until it reaches the coolant temperature incremental
proportion KTW.
For this reason, changeover of the incremental proportion between KTW and
KAP is performed smoothly without any sudden change, and no bad influence
is exerted upon the stability of the engine or upon the composition of the
exhaust gas.
Moreover, it would also be acceptable to utilize either the calculation
process shown in FIG. 3 for the first embodiment or the calculation
process shown in FIG. 4 for the second embodiment in the calculation in
the step S15 of the target supplementary air incremental proportion KAP.
Accordingly, although this invention has been shown and described in terms
of the preferred embodiment thereof, it is not to be considered as limited
by any of the perhaps quite fortuitous details of said embodiment, or of
the drawings, but only by the terms of the appended claims, which follow.
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